The clinical impression that patients with hypertrophic cardiomyopathy and coronary artery disease had higher mortality rates and different septal morphology than HCM patients without coronary artery disease was tested by a review of the NHLBI experience. A retrospective study of all patients undergoing left ventricular myotomymyectomy (LVMM) performed as a first-time procedure with or without concomitant coronary artery bypass grafting was undertaken. A total of 415 patients were included. In each patient, age, sex, presence of coronary artery disease, occurrence of ventricular septal defect, hemodynamic data, and echocardiographic data were recorded. Coronary artery disease was considered to be present if 1) more than 75% stenosis of 1 or more extramural coronary artery was noted by coronary angiography, 2) more than 75% stenosis of 1 or more extramural coronary artery was noted at autopsy within 6 months of operation. Coronary artery disease was considered to be absent if 1) normal coronary angiography was documented immediately before or any time after operation, 2) no coronary artery disease could be documented at autopsy, 3) patients were 30 years of age or less. All patients not meeting these criteria were considered to have indeterminate coronary artery disease. Multivariate analysis of the data demonstrated that coronary artery disease was a significant independent predictor of VSD after LVMM. Interestingly, coronary artery bypass increased the likelihood of VSD. Further study of pathologic specimens and results of operative and nonoperative management will be described.